Composition for liquid crystal aligning film, liquid crystal aligning film, liquid crystal displays and liquid crystal display element

ABSTRACT

A composition for a polyimide type liquid crystal aligning film characterized in that a diamino compound constituting polyimide contains one, two or more diamine selected from 4,4&#39;-diaminodiphenyl methane, 3,3&#39;-dimethyl-4,4&#39;-diaminodiphenyl methane, 2,2&#39;-dimethyl-4,4&#39;-diaminodiphenyl methane, 3,3&#39;,5,5&#39;-tetramethyl-4,4&#39;-diaminodiphenyl methane and 4,4&#39;-ethylene di-meta-toluidine.

TECHNICAL FIELD

The present invention relates to a composition for a liquid crystalaligning film, as well as a liquid crystal aligning film, a liquidcrystal displays and a liquid crystal display element obtained by usingthe said composition.

BACKGROUND ART

A STN (super twist nematic) mode, a TFT mode and an IPS mode have beenused in liquid crystal display elements for large-sized displays usefulin notebook-type personal computers and word processors etc. Polyimidetype materials having various constitutions have been proposed asaligning films useful for them (Japanese Patent Application Laid-openNos. 61-205924 and 62-297819).

However, superior characteristics have been required increasinglyheretofore as to liquid crystal aligning films with recent improvementsin characteristics of liquid crystal displays.

Liquid crystal aligning films have been hitherto required to havesuperior electro-optic characteristics such as good aligning propertyand high voltage holding ratio etc., and in recent years fine Vthunevenness formed with in a display plane has become an issue, as liquidcrystals having high dielectric anisotropy have been used for loweringof crystal driving voltage. In particular, there occurs phenomenon thatwater washed traces remain as Vth unevenness when water washing beingcarried out in order to remove dust formed during rubbing of aligningfilms, so that, conventional liquid crystal aligning films cannot beensaid sufficient for decreasing the phenomenon.

As an example of aligning films from which high quality liquid crystaldisplay elements being obtained, there has been proposed a polyimidealigning film which is obtained from 4,4'-diaminodiphenyl methane andcyclobutane tetracarboxylic dianhydride in Japanese Patent PublicationNo. 4-33010. The main component of the film is polyimide resin in whichat least 90 mol % of repeated units in polyimide being constitutingunits expressed by formula ##STR1## wherein R denotes divalent aromatichydrocarbon radical, and the film is superior in its transparency andheat resistance. Therein, 4,4'-diaminodiphenyl methane is said to beeffective as diamine.

Further, in Japanese Patent Application Laid-open No. 4-57027, it wasdisclosed that by using polyimide with poly-condensed structure of acyclobutane tetracarboxylic dianhydride component and a4,4'-diaminodiphenyl methane component as an aligning film, the film hasa high voltage holding ratio and is suitable for an active matrix typeliquid crystal display device.

However, in the case that a substrate of liquid crystal display elementis washed with water in order to remove impurities adhered on a surfaceof an aligning film during preparation of the liquid crystal element,there is a problem that faint washing traces remain at the time oflightening the entire screen of the said liquid crystal display elementin intermediate tone. In particular, washing traces remain clear in thecase that liquid crystals with high dielectric constant being used.

A problem to be solved by the invention is to propose a composition fora liquid crystal aligning film having characteristics hitherto requiredfor an aligning film, such as good aligning property, high voltageholding property and no water washing unevenness when water washingbeing carried out; a liquid crystal aligning film formed therefrom; aswell as a liquid crystal displays and a liquid crystal display elementwith use of them.

DISCLOSURE OF INVENTION

We inventors have taken the problems in the above-mentioned conventionaltechniques into consideration and studied eagerly to find that use ofthe particular polyimide as a liquid crystal aligning film is veryeffective for dissolving the problems and attain the present invention.

That is, the present invention consists of a composition for a polyimidetype liquid crystal aligning film characterized in that a diaminocompound constituting polyimide contains one, two or more diamine(s)selected from 4,4'-diaminodiphenyl methane,3,3-dimethyl-4,4'-diaminodiphenyl methane,2,2'-dimethyl-4,4'-diaminodiphenyl methane,3,3'5,5'-tetramethyl-4,4'-diaminodiphenyl methane and4,4'-ethylene-di-meta-toluidine. Amongst them, it is more preferable touse 2,2'-dimethyl-4,4'-diaminodiphenyl methane and 4,4'-ethylenedi-meta-toluidine since viscosity during polymerization tends toincrease.

Further, the invention consists of a composition for a liquid crystalaligning film characterized in that tetracarboxylic dianhydrideconstituting polyimide according to claim 1 contains more than 20 mol %of cyclobutane tetracarboxylic dianhydride.

Also, the invention consists of a liquid crystal aligning film which isformed from the said composition, as well as a liquid crystal displaysand a liquid crystal display element both having the said liquid crystalaligning film.

Causes of Vth unevenness has not been clear, but it seems that waterabsorbed during water washing remains slightly in a liquid crystalaligning film due to difference in water absorptance of the liquidcrystal aligning film and that Vth unevenness is formed under theinfluence of it as if the water traces remain.

PREFERRED EMBODIMENT

As diamine useful in the invention, there is (are) used one, orcombination of two or more diamine(s) selected from 4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenyl methane,2,2'-dimethyl-4,4'-diaminodiphenyl methane,3,3',5,5'-tetramethyl-4,4'-diaminodiphenyl methane and 4,4'-ethylenedi-meta-toluidine.

The sum of these compounds to be used is preferably 20 mol % or more andmore preferably 50 mol % or more.

Compounds which can be used as diamine other than above-mentioned onesare exemplified as follows: 2,2-bis[4-(4-aminophenoxy)phenyl]propane,2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, m-phenylene diamine,p-phenylene diamine, m-xylylene diamine, p-xylylene diamine,2,2'-diaminodiphenyl propane, 4,4'-diaminodiphenyl ether, benzidine,1,1-bis[4-(4-aminophenoxy)phenyl]cyclohexane,1,1-bis[4-(4-aminophenoxy)phenyl]-4-methyl cyclohexane,1,1-bis[4-(4-aminophenoxy)phenyl]-4-ethyl cyclohexane,1,1-bis[4-(4-aminophenoxy)phenyl]-4-propyl cyclohexane,1,1-bis[4-(4-aminophenoxy)phenyl]-4-butyl cyclohexane,1,1-bis[4-(4-aminophenoxy)phenyl]-4-pentyl cyclohexane,bis[4-(4-aminobenzyl)phenyl]methane,1,1-bis[4-(4-aminobenzyl)phenyl]cyclohexane,1,1-bis[4-(4-aminobenzyl)phenyl]4-methylcyclohexane,1,1-bis[4-(4-aminobenzyl)phenyl]4-ethylcyclohexane,1,1-bis[4-(4-aminobenzyl)phenyl]4-n-propylcyclohexane, 1,1-bis[4-(4-aminobenzyl) phenyl]4-n-butylcyclohexane, 1,1-bis[4-(4-aminobenzyl) phenyl]4-n-pentylcyclohexane; 1,1-bis[4-(4-aminobenzyl)phenyl]cyclohexane, 1,1-bis [4-(4-aminobenzyl)phenyl]-4-methylcyclohexane, 1,1-bis[4-(4-aminobenzyl)phenyl]-4-ethylcyclohexane,1,1-bis[4-(4-aminobenzyl)phenyl]-4-propylcyclohexane,1,1-bis[4-(4-aminobenzyl)phenyl]-4-butylcyclohexane,1,1-bis[4-(4-aminobenzyl)phenyl]-4-pentylcyclohexane,1,1-bis[4-(4-aminobenzyl)phenyl]-4-hexylcyclohexane,1,1-bis[4-(4-aminobenzyl)phenyl]-4-heptylcyclohexane,1,1-bis[4-(4-aminobenzyl)phenyl]-4-octylcyclohexane,1,1-bis[4-(4-aminobenzyl)phenyl]methane.

These compounds may be used alone or in combination of two or morecompounds. And, diamines are not limited to these constitutions if thepresent object being attained.

As tetracarboxylic dianhydride, it is preferable to use cyclobutanetetracarboxylic dianhydride in a proportion of 20 mol % or more. Morepreferably, the proportion is 20 to 79 mol %. In the case of above 79mol %, there is a tendency to occur image sticking of both sides.

It is possible to use jointly aromatic tetracarboxylic dianhydrides,alicyclic tetracarboxylic dianhydrides and aliphatic tetracarboxylicdianhydrides, unless they damage the characteristics of the invention.

Concretely, the following aromatic tetracarboxylic dianhydrides may bementioned:

aliphatic and alicyclic tetracarboxylic dianhydrides such as ethylenetetracarboxylic dianhydride, decahydronaphtalene-1,4,5,8-tetracarboxylicdianhydride,4,8-dimethyl-1,2,3,5,6,7-hexahydronaphtalene-1,2,5,6-tetracarboxylicdianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride,butane-1,2,3,4-tetracarboxylic dianhydride,bicyclo(2,2,2)-oct(7)-ene-2,3,5,6-tetracarboxylic dianhydride,cyclohexane-1,2,5,6-tetracarboxylic dianhydride,3,3'-bicyclohexyl-1,1',2,2'-tetracarboxylic dianhydride,2,3,5-tricarboxy cyclopentyl acetic dianhydride,5-(2,5-dioxotetrahydrofural)-3-methyl-3-cyclohexene-1,2-dicarboxylicdianhydride,1,3,3a,4,5,9b-hexahydro-5-tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2,-c]-furan-1,3-dione,3,5,6-tricarboxynorbornane-2-acetic dianhydride, 2,3,4,5-tetrahydrofurantetracarboxylic dianhydride;

aromatic tetracarboxylic dianhydrides such as 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyl sulfone tetracarboxylicdianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride,2,3,6,7-naphthalene tetracarboxylic dianhydride, 3,3',4,4'-biphenylether tetracarboxylic dianhydride, 3,3',4,4'-dimethyldiphenyl silanetetracarboxylic dianhydride, 3,3',4,4'-tetraphenyl silanetetracarboxylic dianhydride, 1,2,3,4-furan tetracarboxylic dianhydride,4,4'-bis(3,4-dicarboxyphenoxy)diphenylsulfidedianhydride, 4,4'-bis(3,4-dicarboxyphenoxy) diphenyl sulfone dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy) diphenyl propane dianhydride,3,3',14,4'-perfluoropyridene diphthalic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, bis(phathalic) phenyl sulphine oxidedianhydride, p-phenylene-bis(triphenyl phthalic) dianhydride,m-phenylene-bis(triphenyl phathalic) dianhydride, bis(triphenylphathalic)-4,4'-diphenyl ether dianhydride, bis(triphenylphathalic)-4,4'-diphenyl methane dianhydride and pyromelliticdianhydride.

These compounds may be used alone or in combination of two or morecompounds.

Further, in a composition for a liquid crystal aligning film accordingto the invention, an amino silicone compound or a diamino siliconecompound may be introduced in order to increase adhesion onto asubstrate.

As amino silicone compounds, there may be mentioned para-aminophenyltrimethoxy silane, para-aminophenyl triethoxy silane, meta-aminophenyltrimethoxy silane, meta-aminophenyl triethoxy silane, aminopropyltrimethoxy silane and aminopropyl triethoxy silane.

As diamino silicone compounds, there may be mentioned1,3-bis(3-aminopropyl)-1,1,1-tetraphenyl siloxane,1,3-bis(3-aminopropyl)-1,1,1-tetramethyl disiloxane and1,3-bis(4-aminobutyl)-1,1,1-tetramethyl disiloxane.

N,N-dimethyl formamide, N,N-dimethyl acetamide, N-methyl-2-pyrolidone,dimethyl sulphoxide, hexamethyl phosphoramide, phenol, tetrahydrofuran,dioxane, γ-butyrolactone etc. are preferable as polar organic solventsused in carrying out reaction to obtain a polymer, a resin component forthe liquid crystal aligning film according to the invention, wherein twoor more solvents maybe used jointly.

Further, it is possible to use conventional solvents such as 2-alkoxyethanol type, carbitol type, toluene and xylene etc. together with thesepolar organic solvents, in such a range that solubility of polyimideresin or its precursor being not lowered.

Further, it is also possible to use polymers such as polyamic acids,polyimides, polyesters, polyamides and acrylic polymers etc. within arange not damaging characteristics of the present polymers.

The liquid crystal aligning film according to the invention is convertedto polyimide by heating at 100 to 400° C. and/or treating chemicallywith a dehydrating agent such as acetic anhydride etc. The liquidcrystal display element is prepared by arranging an electrode at a sideagainst liquid crystals on a substrate for a liquid crystal displays andforming a liquid crystal aligning film on the said substrate and theelectrode.

Forming of polyimide layer according to the invention on the liquidcrystal substrate is carried out by applying the above-mentionedcomposition for liquid crystal aligning film on the glass substrate withthe already formed transparent electrode such as ITO (Indium Tin Oxide)etc. and thereafter drying or dehydrating for ring-closure to apolyimide layer. As applying methods, there may be mentioned a printingmethod, a sintering method and a blowing method etc. Dehydratingtemperature for ring-closure can be optionally selected within a rangeof 100 to 400° C., preferably 150 to 330° C. Further, heating time is 1minute to 6 hours, preferably 1 minute to 3 hours.

In order to improve adhesion with the glass substrate, a coupling agentsuch as a silane coupling agent and a titanium coupling agent may beused jointly in the polyimide layer of the present aligning film.

The thus formed polyimide layer is used as a liquid aligning film byrubbing the surface. It is possible to obtain a liquid crystal displayelement by any known method with use of the liquid crystal displaysubstrate having the liquid crystal aligning film.

As liquid crystals used for a liquid crystal display element,fluorine-type liquid crystals are preferable but not particularlylimited to them such as in the case of liquid crystals mixed with liquidcrystals of high dielectric anisotropy other than fluorine-type ones.

Generally, as to the identical fluorine-type liquid crystals, if liquidcrystals having higher driving voltage (lower dielectric anisotropy(Δε)) are used, stained display unevenness due to water washing isdifficultly formed even by using the identical aligning film, and alsoif liquid crystals having lower driving voltage (dilectric anisotropy of6 or more) are used, unevenness due to water washing tends to beeminent.

In the case that a composition for a liquid crystal aligning filmaccording to the invention being made to a liquid crystal displayelement, of course, fluorine-type liquid crystals having less dielectricanisotropy are effective for improvement of the problems, but anyeminent difference is difficultly occurred. However, since more cleardifference appears by use of liquid crystals having dielectricanisotropy of above 6, it is still effective to combine such liquidcrystals for making most of characteristics of a composition for aliquid crystal aligning film according to the invention.

The liquid crystal aligning film according to the invention can be usedin a liquid crystal display element for a large-size display such as aSTN mode, a TFT mode and an IPS mode etc.

If the composition for a liquid crystal aligning film according to theinvention is used for the liquid crystal aligning film and the liquidcrystal display element, unevenness due to water washing can be lowered,which in turn appears eminently particularly in the case offluorine-type liquid crystals with dielectric anisotropy of 6 or more.

The invention is illustrated by the following Examples, but the range ofthe invention is not limited by these Examples.

Occurrence of Vth unevenness formed by water washing is determined asfollows.

A glass substrate having a formed liquid crystal aligning film on an ITOelectrode was subjected to rubbing treatment, and 0.01 ml of ultra purewater was dropped at four points per 4 cm×4 cm and let alone for 5minutes. Thereafter, water drops were washed lightly with ethanol andthen dried at 110° C. for 30 minutes to form a normally black TN panelwith a twist angle of 90° and a cell thickness of 6 μm.

After pouring liquid crystals, direct current voltage by which traces ofwater drops being most violently seen was applied on the panel, and thenpresence or absence of water drops and shade of color were confirmedvisually.

SYNTHETIC EXAMPLE 1

Into 100 ml four-necked flask equipped with a thermometer, a stirrer, aninlet for introducing raw materials and an inlet for introducingnitrogen gas, 1.395 g (7.04 mmol) of 4,4'-diaminodiphenyl methane, 1.697g (7.04 mmol) of 4,4'-ethylene di-meta-toluidine and 94 g (7.04 mmol) ofdehydrated N-methyl-2-pirrolidone were introduced, and stirred under drynitrogen gas stream to dissolve them. While the temperature of thereaction series being maintained below 20° C., 1.535 g (7.04 mmol) ofpyromellitic dianhydride and 1.380 g (7.04 mmol) of cyclobutanetetracarboxylic dianhydride were added and reacted for 15 hours, toobtain a solution of polymer A having a 1:1:1:1 molar ratio of4,4'-diaminodiphenyl methane, 4,4'-ethylene di-meta-toluidine,pyromellitic dianhydride and cyclobutane tetracarboxylic dianhydride aswell as a solid concentration of 6 wt %. Viscosity at that time was 72mPa.s (with use of E type viscosimeter, 25° C.), and weight averagemolecular weight was 95 thousands (determined by gel permeationchromatography, and so forth).

SYNTHETIC EXAMPLE 2

By the same method in Synthetic Example 1 except for using2,2'-dimethyl-4, 4'-diaminodiphenyl methane instead of 4,4'-ethylenedi-meta-toluidine, a solution of polymer B having a 1:1:1:1 molar ratioof 4,4'-diaminodiphenyl methane, 2,2'dimethyl-4,4'-diaminodiphenylmethane, pyromellitic dianhydride and cyclobutane tetracarboxylicdianhydride as well as a solid concentration of 6 wt % was obtained.Viscosity at that time was 60 mPa.s (with use of E type viscosimeter, at25° C.), and weight average molecular weight was 82 thousands.

SYNTHETIC EXAMPLE 3

By the same method in Synthetic Example 1 except for using3,3'-dimethyl-4,4'-diaminodiphenyl methane or3,3',5,5'-tetramethyl-4,4'-diaminodiphenyl methane instead of4,4'-ethylene di-meta-toluidine, a solution of polymer C having a1:1:1:1 molar ratio of 4,4'-diaminodiphenyl methane, 3,3-dimethyl-4,4'-diaminodiphenyl methane, pyromellitic dianhydride andcyclobutane tetracarboxylic dianhydride as well as a solid concentrationof 6 wt %, and also a solution of polymer D having a 1:1:1:1 molar ratioof 4,4'-diaminodiphenyl methane,3,3',5,5'-tetramethyl-4,4'-diaminodiphenyl methane, pyromelliticdianhydride and cyclobutane tetracarboxylic dianhydride as well as asolid concentration of 6 wt % were obtained. Viscosity of the polymer Csolution at that time was 58 mPa.s (with use of E type viscosimeter, at25° C.) and weight average molecular weight was 72 thousands, as well asviscosity of the polymer D solution was 67 mPa.s (with use of E typeviscosimeter, at 250° C.) and weight average molecular weight was 86thousands.

SYNTHETIC EXAMPLE 4

By the same method in Synthetic Example 1 except for using only4,4'-diaminodiphenyl methane as a diamino compound, a solution ofpolymer E having a 2:1:1 molar ratio of 4,4-diaminodiphenyl methane,pyromellitic dianhydride and cyclobutane tetracarboxylic dianhydride aswell as a solid concentration of 6 wt % was obtained. Viscosity of thepolymer E solution at that time was 65 mPa.s (with use of E typeviscosimeter, at 25° C.), and weight average molecular weight was 115thousands.

EXAMPLE

Solutions obtained in Synthetic Examples 1 to 4 were diluted to 3 wt %with 2-butoxy ethanol and applied on glass substrates with the formedtransparent electrodes by a spinning coating method, and then convertedinto polyimides by heat treatment at 200° C. for 1 hour, so that thinfilms with film thickness of about 60 nm were formed (herein, polyimidesobtained from polymers A, B, C, D and E being referred to A, B, C, D andE, respectively). The said polyimide thin films were subjected torubbing treatments to make the aligning films. By using substrates withformed aligning films, the liquid crystal cells having a twist angle ofnematic layer of 90° and a thickness of the liquid crystal layer of 6 μmwere made. The specified liquid crystals were poured into the saidliquid crystal cells and used for experiments after heat treated at 110°C. for 30 minutes.

In these experiments, two kinds of liquid crystals having differentmagnitudes of dielectric anisotropy were used. Compositions and physicalproperties of liquid crystals 1 and 2 are shown as follows.

Liquid crystal 1 ##STR2## Physical properties

NI point 80.2° C.

viscosity at 20° C. 23.3 mPa.s

Δn 0.0965

ΔE 5.7

Liquid crystal 2 ##STR3## Physical properties

NI point 79.9° C.

viscosity at 20° C. 26.28 mPa.s

Δn 0.0841

Δε 9.9

Results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        occurrence level of Vth unevenness                                            ______________________________________                                        A    liquid crystals 1                                                                          water drop trace could not be observed                           liquid crystals 2                                                                          water drop trace could not be observed                      B    liquid crystals 1                                                                          water drop trace could not be observed                           liquid crystals 2                                                                          water drop trace could not be observed                      C    liquid crystals 1                                                                          water drop trace could not be observed                           liquid crystals 2                                                                          slight water drop traces could be observed                                    difference in voltage between water drop                                      traces and normal parts; about -8 mV                        D    liquid crystals 1                                                                          water drop trace could not be observed                           liquid crystals 2                                                                          water drop trace could not be observed                      E    liquid crystals 1                                                                          water drop traces could be observed                                           difference in voltage between water drop                                      traces and normal parts; about -23 mV                            liquid crystals 2                                                                          clear water drop traces could be observed                                     difference in voltage between water drop                                      traces and normal parts; about -54 mV                       ______________________________________                                    

From the experiments, it is clear that the liquid crystal displayelements can be obtained by using compositions for liquid crystalaligning films in Synthetic Examples 1 to 3, in which stainy displayunevenness is difficultly produced after water drops being adhered onthe surfaces of the aligning films.

Industrial Applicability

The liquid crystal display element with use of the compound according tothe invention becomes more difficult to produce stainy displayunevenness formed after water washing of the aligning film than the casethat liquid crytals of higher dielectric anisotropy being used.

The liquid crystal display elements according to the invention are quitesuitable particularly for active driving type liquid crystal displaydevices of high quality and large volume display, so that they may beused in liquid crystal display devices for terminals of OA machineriesand display devices to be mounted in automobiles.

What is claimed is:
 1. A polyimide for a liquid crystal aligning filmformed from at least 20 mol % of a diamine, 20 to 79 mol % cyclobutanetetracarboxylic dianhydride, and the remainder mol % being pyromelliticdianhydridediamine, said diamine selected from the group consisting of4,4'-diaminodiphenyl methane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 2,2'-dimethyl-4,4'-diaminodiphenyl methane,3,3',5,5'-tetramethyl-4,4'-diaminodiphenyl methane, 4,4'-ethylenedi-meta-toluidine and mixtures thereof.
 2. A liquid crystal aligningfilm which is formed from a polyimide for a liquid crystal aligning filmaccording to claim
 1. 3. Liquid crystal display having a liquid crystalaligning film according to claim
 2. 4. A liquid crystal display elementcomprising a polyimide liquid crystal aligning film according to claim 1on a substrate having transparent electrode thereon.
 5. A liquid crystaldisplay element according to claim 4, wherein said liquid crystaldisplay element further includes a liquid crystal composition having afluorine atom, said liquid crystal composition having dielectricanisotropy of 6 to 14.